The present invention relates to a thermoplastic hot melt adhesive which is capable of bonding similar and dissimilar substrates, provides a seal for moisture vapor permeability in the temperature range between -30.degree. C. to 90.degree. C. and is particularly suitable for bonding automotive head lamp and tail lamp lenses to the reflector housing as no fogging of the lamp lens occurs during the bonding process.
While a wide range of uses for hot melt adhesive compositions are known throughout the automotive industry, it has been found that a hot melt adhesive for bonding in a particular use or application may be completely unsuitable for other uses or applications. Thus, various hot melt adhesive compositions have been proposed for use in the automotive industry for bonding automotive head lamp and tail lamp lenses to the reflector housing. The adhesive must possess certain physical properties for this particular application. The adhesive must exhibit good adhesion to glass, polycarbonate, acrylates, polyesters and aluminum, good flow resistance up to 90.degree. C., resistance to moisture vapor permeability, high tensile strength and high elongation, good flow characteristics at 170.degree. C. and quick bond formation upon cooling to room temperature.
U.S. Pat. No. 4,835,200 discloses a color stable hot melt adhesive composition useful for product assembly applications such as multiline adhesive used in the construction of disposable diapers, sanitary napkins and bed pads. The adhesive composition contains a block copolymer prepared using a bromide based coupling agent, a tackifying resin and a stabilizer composition containing a thio compound, a phenolic antioxidant, a tris-(nonylated phenyl)phosphite and an aliphatic compatible epoxy compound.
It is a primary object of the present invention to provide a thermoplastic hot melt adhesive suitable for bonding automotive head lamp and tail lamp lenses to the reflector housing.
Further objects and advantages of this invention will become apparent from the following descriptive material and illustrative examples.